Color photography



Feb. 11, 1936. T. T. BAKER 'coLoR PHOTOGRAPHY Filed May 28, 1934 E an R6N T E E E D mm M w :IIV VTOFI 29/%%,M-.MM

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Patented Feb. 11, 1936 UNITED STATES PATENT OFFICE COLOR PHOTOGRAPHYApplication May as, 1934, Serial No. 728,031 In Great Britain June 6,1933 Claims. (01. 95-815) This invention consists in improvements in orrelating to color photography. It has already been proposed (for examplein United States Patent No. 1,805,361) to produce a multi-color 5 screenon films or plates for use in color photography or color cinematographyby a process in which a-series of lines of greasy ink are applied to thefilm or plate by means of an engraved roller. It is found in practice,however, that such a roller is diificult and expensive to make andparticularly so if more than 20 lines and 20 intervening grooves permillimetre are required. The screen produced by the process using anengraved roller consists of regular lines or squares of coloredelements, and it is found diflicult to engrave a roller of sufiicientfineness having the lines and grooves or other pattern of non-regularformation. It is, however, desirable that the color screen shall consistof irregularly arranged elements in order that the eye may not easilydisoern the elements and in order to minimize interference effectsbetween the color screens when printing. It is among the objects of thepresent invention to provide a method for producing a color screenhaving fine elements, and, if desired,

.of non-regular shape or in non-regular formation.

It has already been proposed to use printing surfaces having mercurialink repelling areas, and it has now been found that such a method isparticularly applicable to the production of color screen films orplates.

The present invention provides the process of making a multi-colorscreen for color photography or cinematography which comprises applyingone color, or colored layer, to the surface of a film or other suitablebase, applying a pattern of greasy resist to the colored surface bymeans of a printing surface (e. g., a roller) having mercurial inkrepelling areas, bleaching the color from the portions of the coloredsurface unprctected by the resist, dyeing the bleached portions a secondcolor and removing the resist. Preferably the steps of applying theresist by means of a printing surface having mercurial ink repellingareas, bleaching the color from the portions of the-colored surfaceunprotected by the resist, dyeing the bleached portions and removing theresist are repeated to form a threeor four-color screen.

When it is desired to produce a screen having the elements innon-regular formation or nonregular shape, the ink repelling areas ofthe resist applying roller are non-regular in form or arrangement. butare. of course, so proportioned as to provide the desired ratio betweenthe total areas of the several colors in the finished screen. Theinvention includes a photographic film or plate having a multi-colorscreen when produced by' the above described method. 5

A description of one method of carrying the invention into elfect in theproduction of cinematograph films for use in making pictures innaturalcolors will now be described by way of example with reference tothe accompanying 10 drawing in which:-

Figures 1 to 6 are diagrams to a very greatly increased scale of thescreen in various stages of its preparation,

Figure 7 is a section of the printing roller em- 5 ployed and Figure 8is a diagrammatic development of a portion of a printing roller used forthe first resist applying step. v

A cellulose acetate film is produced in any 20 known way, but,preferably, according to the methods described in British Patent No.287,635 and United States Patents Nos. 1,811,689 and 1,666,377. Thethickness of the film may be about 0.0055 inch, and the filmisconveniently coated on a width of about 21 or of about 42 inches. Theclean film, from a bobbin, is led through a coating apparatus,preferably of the type described in United States Patent No. 1,929,877.The object isto apply on one side of 30 the film a fine layer ofcollodion of a definite and uniform thickness, which embodies one of thethree primary color dyes for example, the green dye. It is thiscollodion coating which is to receive the various dyes, and indetermining 35 the composition of the collodion and the thickness of thelayer the determining factor is that the ultimate colored portions shallgive the correct spectrum absorption. Solutions of indus' trialcollodions of different nitro-cottons are 40 mixed together in suchquantities as to afiord the required viscositythe proportions beingvaried to suit the temperature, humidity, and similar conditions. Thecollodion mixture is dyed green with an alcoholic solution of malachitegreen 45 and of .auramine. The composition of the dye may be, forexample, alcohol parts, malachite green 4 parts, auramine 6.7 parts andthe composition of the collodion mixture may be, for example, collodionmixture 30 cc. dye solution 2 50 cc. For instance, in practice it hasbeen found convenient to apply this solution in such a thickness that anarea of 100 c. long W26 0. wide, takes 22 to 25 cc. Thus, the thicknessof the layer is.about..01 millimetre wet, i. e., .0002 to 55 .0005millimetre when dry. Alternatively the collodion layer may be put onuncolored and thereafter dyed.

The film dyed uniformly green all over is then led through a printingmachine by means of which an extremely fine irregular pattern of greasyink (intended to act subsequently as fatty resists) is printed upon it.The film at this stage is as shown in Figure 1.

' The printing is effected by means of a steel or other roller havingextremely fine chromium inking areas I and mercurial ink repelling areas2 as shown diagrammatically in Figure 8. The roller a section of whichis indicated in Figure 7 is produced by the known method of plating aroller with silver as indicated at 3 and then with chromium as at 4 andthen coating the plated surface with bi-chromated gelatin,photographically printing onto the gelatin a series of lines (or otherfigures) and developing the figures with hot water, etching away thechromium from the parts of the roller unprotected by the hardenedgelatin and treating such parts with mercury so as to form anink-repelling amalgam with the underlying silver. It is found that theamalgam is strongly repellant to greasy ink, but that the chromiumsurface will retain the ink and transfer it to the film. When it isdesired to print a resist in any particular pattern, it is onlynecessary to produce an enlarged model of the pattern and to reduce itphotographically on to the bi-chromated gelatin. A roller hearing thispattern may thenbe produced as described.

After an interval of about an hour, to let the ink dry, the film is ledin succession (a) over a bath which bleaches and dissolves out the greendye from only the clear spaces, leaving unattacked the green areasprotected by the ink. The com: position of this bath is Alcohol 100parts,

(b) over an inking roller which applies a red dye to the spaces betweenthe ink areas leaving the film as shown in Figure 2. In this example,the red dye is basic red N Extra (Kuhlmann) 8% solution in alcohol. Thefilm is thoroughly washed with water to remove the excess of dye. (c)The filmis passed through a solvent cleansing bath of benzene and isbrushed by roller brushes within the benzene to remove the ink areas,leaving exposed the clear green areas. The film at this stage has equalareas of red and green and is as shown in Figure 3.

The film is again led (when dry) through the printing machine whichproduces areas of greasy ink, as before, but this time the areas of inkoccupy about two-thirds of thearea of the film as shown in Figure 4 andfall indiscriminately on the red and green areas previously formed.

After an interval for the ink to dry, the film is led in succession (a)over a bath which bleaches and dissolves out the red and green dye fromonly the clear spaces between the greasy areas, (b)v over an inkingroller which applies a violet dye which dyes the spaces leaving the filmas shown in Figure 5. The violet dyecontains- Crystal violet (4%solution in alcohol) parts, and malachite green (8% solution in alcohol)20 v parts.

(c) The film is again led through a solvent cleansing bath of benzeneand is brushed by rollerbrushes within the benzene to remove the inkareas and leave the completed screen as shown Alcohol parts,

Caustic potash (10% aqueous solution) 1 part, Acetone 10 parts,

Water 6' parts.

In the above example the ink areas applied and the resulting areas ofcolor on the film are irregular in shape and arrangement but if desiredthe invention may be a plied to the production of a screen havingregular areas (e. g. lines or squares). In one example of this form ofthe invention the roller has 25 chromium lines and 25 repellantmercurial spaces per millimetre at an angle of 23 to the axis of theroller and the same roller is used for both applications of the resistmaterialthe lines of the second application being applied at rightangles to those of the first. The last applied color in this exampleoccupies a total area on the screen equal to the sum of the areas of thefirst two colors whereas in the first example described the areasoccupied by all the colors were substantially equal. It will beappreciated that'the present invention provides a method whereby anydesired relation between the total area's occupied by the severalcolors-may be easily obtained, and thus any desired color balancebetween the colors can be attained.

It will be seen that by the above process it is possible to produce amulti-color screen having extremely fine elements or having elements ofirregular shape or arrangement which need not in practice be so fine asthose of regularshape.

I claim:-

1. The process of making a multi-color screen for color photographywhich comprises applying one color to the surface of a suitable base,ap-

plying a pattern of inky resist to the colored surface by means of a.printing surface having mercurial ink-repelling areas, bleaching thecolor from the portions of the colored surface unpro-' tected by theresist, dyeing the bleached portions a second color and removing theresist.

2. The process of making a multi-color screen for color photographywhich comprises applying one color to the surface of a suitable base.

applying a pattern of inky resist in irregular figures to the coloredsurface by means of a printing surface having mercurial, ink-repellingirregular areas, bleaching the color from the portions of the coloredsurface unprotected by the resist, dyeing the bleached portions a secondcolor and removing the resist.

3. The process of making a three-color screen for color photographywhich comprises applying one color to the surface of a suitable baseapplying,

a pattern of inky resist to the colored surface by means of a printingsurface having mercurial ink-repelling areas. bleaching the color fromthe portions of the colored surface unprotected by the resist, dyeingthe bleached portions 2. second color and removing the resist, againapplying a pattern of inky resist to the colored surface, and out ofregister with the pattern produced as above. by means of a printingsurface having mercur al ink-repelling arew, bleaching the color fromthe portions of the colored surface unprotected by the resist, dyeingthe bleached portions and removing the resist.

4. The process oi making on a suitable has a multi-color screen forcolor photography which comprises applying a coating of cellulosenitrate in solution to the base, dyeing the coating uniformly with onecolor, applying a pattern of inky resist to the coating by means of aprinting surface having mercurial ink-repelling areas, bleaching thecolor from the portions of the coating unprotected by the resist; dyeingthe bleached portions a second color and removing the resist.

5. The process of making on a suitable base a multi-color screen forcolor photography which comprises applying a coating of coloredcellulose nitrate in solution to the base, applying a pattern ofirregular figures of inky resist to the coating by means of a rollerprinting surface having mercurial ink-repelling irregular areas,bleaching the color from the portions of the coating unprotected by theresist, dyeing the bleached portions a second color and removing theresist.

' THOMAS THORNE BAKER.

